This application is based upon, and claims priority from, Swedish applications Nos. 9703732-9 filed Oct. 14, 1997 and 9703904-4 filed Oct. 27, 1997, both of which are hereby incorporated by reference.
The invention relates to a method and apparatus for introduction of a first fluid into a second fluid, where the second fluid flows in a conduit, and wherein the apparatus includes a first member with a pass-through canal for said second fluid. The first member preferably is arranged to form a section in said conduit, and the apparatus includes one or more chambers that extend around at least a main longitudinal part of the periphery of the pass-through canal. A wall is provided between the inner part of the chamber and the pass-through canal, and means are provided for sustaining a higher pressure in the chamber than in the pass-although canal, the pressure sustaining means for supplying the first fluid to said chamber from a pressurized source.
Methods and apparatus of the above mentioned general kind are known from, for example, SE 468 341 and SE 502 393. The apparatus which is described in SE 502 393 is frequently used as a mixer in the bleaching departments of the cellulose industries, for the mixing of steam into a pulp suspension to a increase the temperature of the pulp to a level which is desirable for a certain reaction to occur at a desired rate in a subsequent bleaching step. The apparatus permits a good mixing of steam into the pulp suspension, but it is hard to control the amount of steam that is mixed-in or added for regulation of the temperature, without concurrently decreasing the effectiveness of the mixing step. The mixing-in of steam is conventionally regulated by means of a valve in the steam line to said chamber. When the steam supply is throttled down in order to reduce the rate of mixing-in of the steam, the pressure in the chamber will, however, also decrease, and hence cause a pressure differential between the inner part of the chamber and the pulp suspension in the conduit. This pressure differential will, in turn, result in a decrease in the velocity of the steam, when it enters the pass-through conduit for the pulp, with the further result of a decrease in the penetration of the steam into the pulp suspension.
It is also typical for known apparatus of the kind heretofore described, and the method which is practiced using such apparatus, that the pass-through conduit is made as a thin, ring shaped passage for the second fluid, which is thought to promote a good mixing-in effect. Without deciding on whether this assumption is right or not, or if it possibly is true under certain special conditions, it can, however, be concluded that the construction, in practice, will lead to certain problems. This would probably depend on the fact that the first fluid, when it is injected at a high velocity in the second fluid which flows through the narrow gap, interacts with the constriction body which is arranged in the pass-through conduit and serious vibrations can develop in the apparatus, probably due to resonance phenomena.
Yet another draw-back with known apparatus of the type heretofore mentioned (and the method practiced using such apparatus) is that they are relatively heavy. The total cost of the apparatus will be high, due to the material normally consisting of high quality stainless steel, and the apparatus moreover being relatively hard to manufacture.
The object of the invention is to provide a method and apparatus, which is not afflicted with the above mentioned limits or draw-backs. More specifically, the present invention is directed to a method and apparatus which provides an effective mixing-in of a first fluid into a second fluid, which enables regulated mixing-in of the first fluid with sustained, good mixing-in of the first and second fluids under a wide range of temperature, pressure and fluid velocity conditions, which is easy to automate to achieve the right mixing-in, which is easy to manufacture and which is easy to assemble. Another positive effect of the present invention is that the method and apparatus develops relatively few vibrations. The invention aims, in principle, to achieve a regulation function for adjustable mixing-in of a first fluid into a second fluid.